In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
Austenitic steel with optimized properties is used in many different applications and is a common alternative to, for instance, nickel-base alloys. The disadvantage with the latter is the elevated price for the raw material needed to make these alloys.
Primarily, the choice of steel grade is determined by the requirements of corrosion resistance, workability as well as structural stability. Highly alloyed austenitic stainless steels are found in a range of different embodiments for corrosive environments within, for example, the chemical industry, especially in the production of organic and inorganic acids for the production of oil products and for seawater cooling.
The use is, to a large extent, limited by the corrosion resistance. Also, high alloying levels cause problems with both the workability by hot-extrusion and cold-rolling, as well as a decrease in structural stability. These problems are observed with increasing alloying levels of, in particular, the elements Cr, Mo, N, W, Cu and Mn.
The developed alloys are generally characterized in that one tries to find a composition which obtains high corrosion resistance within a broad range of chemical environments. The high alloying levels come with a high price compared to lower alloyed material. In particular, nickel-base alloys are considered as being very expensive. Highly alloyed austenitic alloys with a lower content of nickel but with a high alloying level are frequently limited by their workability, which means that it is difficult to hot-extrude seamless tubes of the alloy or cold-roll the material to suitable final dimension.
The high price means that the market for these types of alloys is relatively limited. Thus, there is a need to develop an all-round material in order to be able to offer a type of alloy for different applications, and offers advantages in the form of cost savings for production and stock-keeping.
It is a disadvantage with the known highly alloyed austenitic steel grades, such as SE 465373, which is hereby incorporated by reference, or nickel-base alloys such as Alloy 59, that structural stability can only be managed within a very narrow temperature range, which causes problems with the production of heavier structures. In addition, subsequent treatment such as welding becomes more complicated. Deteriorated structural stability entails deteriorated corrosion resistance and shorter life time for products produced of these alloys in applications for use in environments requiring the above-mentioned properties.